The present invention relates generally to bandwidth allocation between voice and data traffic in a telecommunications transport system, and in particular to bit-level control for dynamic bandwidth allocation in a channelized digital network transport system.
Transport protocols have been defined to carry both traditional Pulse Code Modulated (PCM) voice traffic as well as packetized data traffic. Within such protocols, it is desirable to dynamically allocate the bandwidth of the transport channel between the voice and data traffic as a function of the voice activity. In general, protocols to handle dynamic bandwidth assignment between the voice and data traffic have been message-based systems. In a message-based system, one end sends a message through an overhead channel to the other end to coordinate changes in bandwidth allocation.
There are drawbacks to message-based control of bandwidth allocation between voice and data traffic. Messages can be lost and/or corrupted in transmission. When a message is lost, the two ends become out of sync as to how to allocate the bandwidth. To overcome this problem, message-based systems often employ methods such as acknowledgements, repeating of messages and periodic maintenance messages to assure that both ends are in agreement as to the bandwidth allocation.
Another issue with message-based systems concerns the speed at which the message can be transferred to affect a change in bandwidth allocation. Standards specify time limits for how long it can take to set up a voice channel after a signaling event, e.g., a subscriber line going off-hook. Standards may allow only 50 ms between the signaling event and the time the channel must be available for voice traffic. Depending on the bandwidth of the message channel, a change in bandwidth allocation may not meet the 50 ms deadline. Even if the bandwidth of the message channel is sufficient, the channel may be shared with other applications that may create added delay for queuing of the message before transmission.
Another example of dynamic bandwidth allocation is described in U.S. Pat. No. 6,009,106 issued Dec. 28, 1999 to Rustad et al. Rustad et al. describe a method for allocating bandwidth between switched (voice) traffic and unswitched (data) traffic over a T1 line using ESF (Extended Superframe) robbed bit signaling. The switched traffic uses its assigned DS0 (digital signal level 0) within the T1 while the switched channel is active. When the switched channel is inactive, the unswitched traffic uses the DS0 that is assigned to the switched channel. The basic premise for the control of the bandwidth allocation is to steal the xe2x80x98Cxe2x80x99 bit in the ABCD signaling information and replace it with a dynamic allocation control bit. The xe2x80x98Cxe2x80x99 bit can be used in this way since with ESF signaling the xe2x80x98Cxe2x80x99 bit is always the same as the xe2x80x98Axe2x80x99 bit. In this manner, the proper signaling information can be recreated once the dynamic bandwidth control information has been retrieved.
When one end of the T1 transport system detects a change in status of the switched channel (for example going from inactive to active), the xe2x80x98Cxe2x80x99 bit value is changed. The data being carried in the DS0 assigned to the switched channel is not changed until the start of the next ESF superframe. At the receiving end, the change in the xe2x80x98Cxe2x80x99 bit value is detected, and the receiving end then knows that on the next superframe boundary the data being carried in the DS0 will change.
While there is benefit to the dynamic bandwidth allocation described in Rustad, et al., Rustad et al. admit that their invention is limited to transmission over a local loop. They note that it is normally inadvisable to utilize the ABCD bits when transmitting data over switched channels across multiple nodes of a telecommunication system. This is because it is possible for frames to be disassembled from one multiframe and reassembled into another multiframe during transmission across a node. As a result, the frames that contain robbed-bit signaling would change during transmission and the relationship between the frame and the robbed bits may be lost.
For the reasons stated above, and for other reasons stated below that will become apparent to those skilled in the art upon reading and understanding the present specification, there is a need in the art for alternative systems and methods for dynamically allocating bandwidth of transport channels between voice and data traffic in a multi-node network environment.
Methods for bit-level control of dynamic bandwidth allocation are adapted for use in multi-node transport systems without regard to the framing mechanisms and multiplexing techniques used by the various nodes in the network. A single status bit is used to indicate the desired allocation status of each channel for which dynamic allocation is permitted or desired. The status bit has a first logic level indicative of a desire to have a first allocation status, such as allocated for voice traffic, and a second logic level indicative of a desire to have a second allocation status, such as allocated for data traffic. The status bit may be repeated multiple times within a frame to mitigate the effects of transmission errors. Spacing the repeated status bits within the frame further mitigates the effects of burst errors. Dynamic bandwidth allocation for multiple channels can be supported by using a separate status bit for each channel.
The status bit or bits are carried within a transport channel, such as a control channel, distinct from the channel(s) subject to dynamic allocation, such as one or more message channels. Message channels can carry voice and/or data traffic depending on the allocation status. In this manner, the values of the status bits can be maintained across node boundaries without regard to the framing mechanisms or multiplexing techniques used by the transport system. A restriction for crossing multiple nodes is that the framing structure support a method which maintains the relationship between the control channel and the message channel(s). The timing relationship must be maintained such that the control and message data be kept in the same frame as the traffic passes through multiple nodes. Also, the spatial relationship must be maintained such that the relationship between the control bits and the message channels they control is preserved as the traffic passes through multiple nodes. The various embodiments described herein thus permit dynamic bandwidth allocation beyond the local loop.
For one embodiment, the invention provides a method of dynamically allocating bandwidth in a multi-node transport system. The method includes detecting a condition indicative of a desire to change an allocation status for a first transport channel (e.g., a message channel) of the transport system, wherein detecting the condition occurs during transmission of a first frame from a first node to a second node of the transport system. The method further includes updating a status bit in a second transport channel (e.g., a control channel) in a second frame for transmission from the first node to the second node. The method still further includes changing the allocation status of the first transport channel in a third frame for transmission from the first node to the second node. The third frame is subsequent to the second frame and each frame carries channel traffic for the first transport channel and the second transport channel. For further embodiments the roles of the first node and the second node are reversed.
For another embodiment, the invention provides a method of dynamically allocating bandwidth in a multi-node transport system having at least a first transport channel (e.g., a message channel) associated with a subscriber line and a second transport channel (e.g., a control channel) distinct from the first transport channel. The method includes detecting a subscriber line condition indicative of a desire to change an allocation status for the first transport channel in an upstream direction from a first node to a second node of the transport system, wherein detecting the subscriber line condition occurs during transmission of a first frame in the upstream direction. The method further includes updating status bit information in the second transport channel in a second frame for transmission in the upstream direction and changing the allocation status for the first transport channel in a third frame for transmission in the upstream direction. The method still further includes evaluating, at the second node, the updated upstream status bit information from the second frame and updating status bit information in the second transport channel in a fourth frame for transmission in a downstream direction from the second node to the first node. The method still further includes changing the allocation status for the first transport channel in a fifth frame for transmission in the downstream direction.
For yet another embodiment, the invention provides a communications transport system for carrying a first traffic type (e.g., voice) and a second traffic type (e.g., data) between a first node and a second node. The transport system includes a carrier for transmitting frames between the first node and the second node, wherein the carrier has at least one first transport channel (e.g., a message channel) and a second transport channel (e.g., a control channel) distinct from each of the first transport channels and wherein each frame carries a sample of each of the first transport channels and the second transport channel. Each frame carries a status bit in the second transport channel corresponding to each of the first transport channels and each status bit is indicative of a desired allocation status for its corresponding first transport channel.
For a further embodiment, the invention provides a method of processing channel traffic in a telecommunications transport system having at least one first transport channel (e.g., a message channel) and a second transport channel (e.g., a control channel) distinct from each of the first transport channels. The method includes receiving a frame containing a sample of the channel traffic from each of the first transport channels and the second transport channel, wherein the second transport channel carries status bit information indicative of a desired allocation status for each of the first transport channels. The method further includes processing the samples of the channel traffic from each of the first transport channels according to their desired allocation status indicated by the status bit information carried by the second transport channel in an earlier received frame.
Further embodiments of the invention include apparatus and methods of varying scope.